1. Field of the Invention
This invention relates to a process for producing 6-hydroxychroman derivatives, more particularly, to a process for producing 2,2,4-trimethyl-6-hydroxy-7-substituted chromans.
2. Description of the Prior Art
It is known that 6-hydroxychroman derivatives are effective as antioxidants for gasoline, oils and fats, and other organic compounds, as described in U.S. Pat. No. 2,535,058. Also, British patent specification No. 1,141,812 discloses that they are effective as agents for preventing the deterioration of a color photographic light-sensitive image due to light irradiation. Further, they are used as agents for preventing the thermal deterioration of polyester resins, as described in Japanese Patent Application (OPI) 30,754/72. The products of the present invention can be used for any of the uses set forth above.
At present, the 6-hydroxychroman derivatives which are useful in many areas are not produced industrially in any volume, because few methods are industrially advantageous for producing the same. For example, U.S. Pat. No. 2,535,058 discloses a method of synthesizing 2,2-dimethyl-6-hydroxychroman by reacting 4-methoxyphenol and isoprene with anhydrous hydrogen chloride in glacial acetic acid at 0.degree. C to form 2-.gamma.-dimethacryl-4-methoxyphenol and then heating the same with hydrogen bromide in glacial acetic acid. However, this method is complicated in operation and equipment since two reaction steps are required.
On the other hand, British patent specification No. 1,141,812 describes a method of synthesizing 6-hydroxychroman derivatives by reacting alkyl-substituted hydroquinones with a conjugated diene compound in the presence of zinc chloride. This method is, however, not advantageous on an industrial scale since the conjugated diene compounds used as a reaction reagent are generally costly.